Pond Boss Forums INTRO Questions & Observations Structural Engineering Question

How much weight can this setup take? The 4x4s span across seven rafters set at 24" centers. The rafters are 40' long. The hoist is a 3 ton.



I was thinking of hoisting my Bass boat up the for the winter (kidding).

Looks like a "Life is Good Barge" lift to me !!

How much does that sucker weigh, Dwight?

I have never used this technique for anything more than maybe 400 lbs. Say 500 lbs counting 4"x4's and a chain fall.

The roof can handle your MN Winter snow load, when distributed. Maybe more, but that what it's been proofed at.

On the plus side, you've got the load distributed over 7 trusses. On the down side, it's not a distributed load wrt each truss - it's a single point application. It has been a long time since I took statics and strengths of materials, but I think the load each truss can handle is maximized when distributed over the whole truss (if it wasn't, they'd build the truss differently so it would still handle the roof + snow weight and be cheaper).

The really BIG downside is that if it's too much weight, the roof is kindling. I haven't done any of this since the building it was in was owned by me, and my wife won't let me do it in her horse barn.

Got access to an engine hoist or a front end loader?

...or vertical supports from the ground to the horz timbers, located as close as possible to the block. Lift and block the steel mass at the outer perimeter (the perimeter blocking has to be VERY close to the same height as the trailer). Then remove the tall vertical supports and back the trailer underneath. Knock out the perimeter supports with a sledge being very careful not to spill the Coronas.

The barge weighs less than 800 pounds. I only plan to use the hoist to tip it over, not to lift it. If you have ever tried to tip over an 8'x16' 800 pound item you understand that it is at least a 3 man job. A couple of them will probably be going to the chiropractor after the tip over.

I used one of those cable hoists to tip it over one time and that seemed more dangerous and a lot slower than a chain hoist.

If you are only lifting one end, max loading will be under 400 lbs. And will occur at the beginning and the end, when the barge frame is level. So if it made it off the ground the worst should be over.

Maybe. But I'm glad I have a front end loader.

In my early years I have yanked out engines and picked up front ends of cars and trucks with only a 3" pipe between two rafters.

In my semi-middle years I added a couple 2x8's and a couple floor jacks, the type you use to support a basement floor or roof, that was a bit safer.

Now I have power equipment that could lift a suburban 16ft up and make it do a nose dive into a pile of concrete.

What went wrong???

Phil, Theo is correct, it is still a point load. The 4*4's will not distribute the load evenly across the trusses. The center truss will take the most load. The 4*4's will bow up on the ends as the middle is loaded. Bretski has a good answer as well.If you insist on going with the set up you have you should spread the chain connections apart at the 4*4's, ie. a spreader bar. This will spread the load more evenly. The bottom cords of the trusses are only rated for 10-15lbs. per sq.ft., depending on your building codes.

Ron

800 lbs should not be a problem, as long as you do not have 14 feet of snow on the roof. It's more stout than you think, just be careful. Add some extra precaution by putting in a post or two to the rafters. Those prefab rafters with the press in plates are really good but they can become fatigued with repeated loading. Think about your safety first!!! a couple extra bucks could go a long way here, and in the future.